Method for activating an electric motor and a metering pump by supplying predetermined pulse intervals to supply predetermined fluid quantities

ABSTRACT

The methods serves for activating an electric motor of a metering pump with which the fluid quantity (V nom ) to be delivered is set by an external impulse trigger, wherein a predetermined delivery quantity (V nom ) is allocated to each impulse (t). The control detects the temporal interval (Δt) of the two last-received impulses and activates the electric motor such that the fluid quantity to be delivered, taking the previously evaluated interval as a basis, is distributed over the subsequent impulse interval.

BACKGROUND OF THE INVENTION

The invention relates to a method for activating an electric motor of ametering pump.

Metering pumps functioning according to the displacement principle, thusthose with a diaphragm or piston pump, are either operatedelectromagnetically or by way of a motor. With electromagneticallyoperated metering pumps the delivery quantity is usually set bymechanical stroke adjustment on the one hand and by frequency change onthe other hand. In order to achieve as accurate as possible metering(admixing) of the fluid into a changeable delivery flow (main deliveryflow), such pumps usually have an electrical connection to which a clockgenerator may be connected which always emits an impulse when a certaindelivery quantity of the main delivery flow has been delivered,whereupon the metering pump executes one or more working strokes whosedelivery stroke is mechanically matched to the metering quantity to bedispensed per impulse. In spite of this matching of the delivery flowsto be mixed, irregular mixing ratios may occur depending on the strokeadjustment and the fluid quantity to be delivered, specifically if, forexample, in a short time the fluid to be metered is to be delivered intothe main flow and the next impulse is only effected after a long periodof time.

Besides metering pumps with an electromagnetic drive constructed withquite a simple design, there are also known those with an electromotoricdrive, for example, from DE 196 23 537 A1. Such metering pumps are muchmore complicated with regard to design, but permit a more exact anduniform control of the delivery quantity. Usually they function withoutstroke adjustment. A metering pump of this construction type is, forexample, known from the type LEW A LAB K3/K5 of LEWA Herbert Ott GmbH &Co. in Leonberg. Although this pump comprises an interface for theexternal metering flow control, here however the activation is effectedvia an analog signal, which is complicated in signal processing andfurther processing, and is also prone to malfunctioning. The meteringdelivery quantity here is controlled in dependence on an electricalcurrent.

BRIEF SUMMARY OF THE INVENTION

Against this state of the art it is the object of the present inventionto design an electromotorically driven metering pump such that with anexternal impulse activation it delivers according to a predefined courseas exactly as possible.

In one aspect, this invention comprises a method for activating anelectric motor of a metering pump, with which the fluid quantity to bedelivered is predefined by way of an external impulse trigger, wherein apredetermined delivery quantity is allocated to each impulse,characterized in that the temporal interval of at least two impulses isdetected and the electrical motor is activated such that the fluidquantity to be delivered, taking the previously evaluated interval as abasis, is distributed over a subsequent impulse interval according to apredefined course.

The basic concept of the present invention is to distribute the quantityto be delivered according to a predefined course over the time intervalformed between two or more impulses, and specifically in a manner suchthat, where possible there is always present a certain deliveryquantity. Usefully, at the same time, the temporal interval of twosuccessive impulses is determined and then the drive of the electricmotor, for example a stepper motor or a direct current or alternatingcurrent motor equipped with suitable sensorics for position detection,is activated such that, for example, there is effected as uniform aspossible distribution of the fluid quantity to be delivered in theimpulse interval subsequent to this or in a subsequent impulse intervalsequence. Within the context of the present invention as uniform aspossible is to be understood for example in that with a stepwiseoperation the steps are distributed over the impulse interval with thesame temporal interval. It is to be understood that a completely uniformdistribution may possibly be upset by one or more required returnstrokes of the pump, even if, as already belongs to the state of theart, the motor during the return stroke is activated at a higher speedthan during the delivery stroke.

If the temporal intervals between the successive impulses becomeshorter, this may lead to the fact that the delivered and metered fluidquantity is smaller that the actually desired quantity. In order toavoid this the invention envisages determining the missed quantityresulting after the activation of two or more successive impulseintervals and correcting this in a later, preferably in the subsequentimpulse interval. Such a correction may be effected in a comparativelymore complicated manner by determining the actual metering delivery flowby way of external sensorics, but is advantageously determined takingthe theoretical metering delivery flow resulting on account of theactivation as a basis, since then no external sensorics are required andthis may be determined by way of the electrical values which in any caseare present internally. Since electromotorically operated metering pumpsdue to their design operate accurately in comparison to the initiallydescribed electromagnetically operated ones, as a rule one may do awaywith external sensorics without having to accept the risk of seriousdisadvantages.

A particular advantage of the impulse control according to the inventionis the ability to do away with the stroke adjustment of the pump bodyknown with pump membranes since this leads to inaccuracies and demands amechanical intervention which makes the remote control of the pumpdifficult.

In particular on admixing a fluid into a changing main delivery flow itis desirable where possible not to let corrections take place at all,but to adapt the metering delivery flow as quickly as possible to thechanging main delivery flow. This may be effected in that with thedistribution of the fluid quantity to be delivered one does not onlytake into account the interval between two or several preceding impulsesand distribute this over a following impulse interval resultingtheoretically there from, but that with this also the change in theimpulse intervals is determined and taken into account when calculatingthe distribution, i.e. a certain control algorithm is effected whichachieves as early as possible adaptation to the changing conditions.

In particular, with metering procedures with which although on the onehand it is a question of as uniform as possible supply to a maindelivery flow and on the other hand of the totally added quantity. i.e.a concentration to be set, as is for example required on admixingchlorine into swimming pool water, it is not only necessary to payattention to a uniform mixture ratio but also to exclude the addition oferrors which may possibly arise due to control inaccuracies or othersources of errors. For this the method according to the inventionenvisages detecting the number of impulses, i.e. the nominal deliveryquantity or a corresponding characteristic variable and comparing thisto the metering delivery quantity which results at least theoreticallyon account of the activation of the electric motor, or to acorresponding characteristic variable, and with differences envisagessubsequently compensating these accordingly. Such a long-term controlmay for example detect the impulses over hours or days in order once perhour or once a day, where appropriate to carry out a supplementarycorrection which may not be fulfilled by a quick control which adaptsthe delivery flow of the metering pump to the changing main deliveryflow.

Irrespective of this long-term control it is basically desirable tocarry out the correction of the detected missed quantity directly afterdetection in order to ensure as quick as possible control. This isparticularly desirable if the metering pump is applied for thecontinuous admixing with which a filling or packaging is effecteddirectly after the admixing, so that later correction no longer have anyinfluence on the already filled or packaged product.

In order to ensure that also at the beginning of the metering procedurethere is already effected a uniform metering over the whole impulseinterval, it is useful to initiate the activation of the pump motor notuntil after the receipt of two impulses. The missed quantity caused bythe method because of this may be compensated by the previouslydescribed overriding correction control.

These and other objects and advantages of the invention will be apparentfrom the following description, the accompanying drawings, and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is hereinafter described in more detail by way of oneembodiment example. There are shown in:

FIG. 1: the dependency of the pulse sequence on the delivery quantity ofa first embodiment example; and

FIG. 2: a second embodiment example in a representation according toFIG. 1,

DETAILED DESCRIPTION OF THE INVENTION

In the drawings on the upper time axis, there is represented a sequenceof electrical impulses t₁ to t₇, as for example are emitted by a clockgenerator, wherein each impulse t₁ to t₇ stands for a certain volume ofa main delivery flow to which a suitable quantity of a metering deliveryflow is to be admixed by way of the metering pump. On the lower timeaxis, there is shown in each case the metering delivery flow controlledby the metering pump in dependence on the external impulses.

In order to achieve as uniform as possible metering of the meteringdelivery flow into the main flow, the metering delivery flow is set byway of the control of the metering pump such that the metering deliveryquantity to be mixed into the main flow is distributed as uniformly aspossible over the whole interval Δt formed between two successiveimpulses. In order to firstly detect the temporal interval Δt, it isnecessary before the beginning of the metering procedure to wait for twoelectrical impulses t₁, and t₂ and to determine the time Δt₁₂ lyingbetween these. Then the pump is activated according to the meteringdelivery quantity to be admixed per impulse such that the volume V_(nom)to be delivered per impulse is distributed over a time beginning at t₂,which corresponds to Δt₁₂, so that taking this time interval Δt₁₂ as abasis there results a delivery flow Q₂₃ which has reached the presetvolume V_(nom) after a delivery time of Δt₁₂. Since in the presentembodiment example the interval of the impulses t₁ to t₄ increases, withthis control, with an increasing interval up to t₄ in each case astoppage of delivery arises for a short time, if specifically the volumeV_(nom) has already been reached, but the subsequent impulse however hasnot been received.

If the control obtains the impulse t₃, it determines the temporalinterval Δt₂₃ to the impulse t₂ and now distributes the quantity V_(nom)to be delivered over this time interval Δt₂₃, thus reduces the deliveryflow Q₃₄ accordingly. The metering delivery flow Q₃₄ results in that onedivides the nominal delivery volume V_(nom) by the last-determined timeinterval Δt₂₃.

If the intervals of the impulses do not become larger, but smaller, asthis is represented by way of the impulses t₄ to t₆, there arises theproblem that a new impulse, for example t₅ is received if the timeinterval for which the delivery flow Q₄₅ has been calculated in order toreach the volume V_(nom) is not yet completed. With the controlaccording to the first embodiment example (FIG. 1) the pump is activatedsuch that on receipt of a new impulse (here t₅ for the first time) theprevious delivery is stopped and for the now newly beginning deliveryinterval Δt₅₆ one fixes a delivery flow Q₅₆ which is calculated suchthat within a time period of Δt₄₅ there results a volume V_(nom) plus avolume V_(rest). The volume V_(rest) results from the volume V_(nom)minus the volume V_(ist) which is actually delivered in the precedinginterval. Thus for the delivery interval Δt₄₅ there results a volumeV_(rest) which results from the delivery flow Q₄₅ multiplied by thedifference of Δt₃₄ and Δt₄₅. This volume which is delivered in the timeinterval Δt₄₅ and which is too low thus is added to V_(nom) oncalculation of the delivery flow volume Q₅₆.

Since the time interval Δt₅₆ again is smaller than the preceding Δt₄₅,the delivery flow Q₅₆ is interrupted after receipt of the impulse t₆ andthen a metering delivery flow Q₆₇ is produced, with which taking adelivery interval of the size order of Δt₅₆ as a basis the delivery flowhas been calculated such that there results a volume which correspondsto the volume V_(nom) plus the volume V_(rest56) not yet delivered inthe delivery interval Δt₅₆. The volume V_(rest56) which has not yet beendelivered at the same time is composed on the one hand of a component ofthe volume V_(nom) which has not yet been delivered in this interval andon the other hand of the not yet delivered component of the volumeV_(rest45) of the further preceding interval, which can be recognised bythe cross-hatching whilst the remaining rest volume is simply hatched.

The previously described control algorithm illustrates the fact that byway of the control one may react quite quickly and exactly to theimpulse even with changing intervals. In practice, the fluctuations ofthe impulse intervals are quite low so that the comparativelycomplicated control represented by way of FIG. 1 is often not at allrequired or may be compensated by an additional overriding correction.Such an overriding correction may follow after a predefined time orafter a predefined number of impulses, wherein the nominal volume to bedelivered within this time corresponding to the impulse number isevaluated and compared to the actual volume resulting on account of thecontrol, and where appropriate is corrected in the subsequent intervalor in the subsequent intervals. Control errors or also controldeviations may be detected over this long-term correction in order toanticipate as much as possible the adaptation to the changing impulseintervals. In practice, control errors, be they due to return strokes orother false strokes, may occur which otherwise are difficult to detector may not be detected at all.

In most cases, however, a simplified control according to the embodimentexample according to FIG. 2 would be sufficient with which the deliveryflow is computed according to the previously described embodimentvariant in which firstly one waits for two impulses t₁ and t₂, the timeperiod Δt₁₂ formed between this is evaluated and the nominal volumeV_(nom) to be delivered per impulse is distributed over this time periodΔ₁₂ so that a delivery flow Q results. In contrast to the previouslydescribed embodiment variant, however, after reaching the delivery flowV_(nom) the delivery procedure is not interrupted but one deliversfurther up to the receipt of the next impulse t₃ in order to ensure acontinuous admixture. The delivery quantity Q₃₄ activated on receipt ofthe impulse t₃ results from the volume V_(nom) to be delivered perimpulse and the time Δt₂₃. The delivery here is also effected up to thereceipt of the next impulse t₄.

As results from this, due to the control, with this embodiment variantwith a reducing impulse sequence too much is delivered, whilst with anincreasing impulse sequence too little is delivered, since in each casethe preset delivery quantity is not corrected until receipt of the nextimpulse. Since the main delivery flow in practice is comparativelyconstant and the deviations fluctuate above and below to the sameextent, one may achieve a comparatively exact metering with thissimplified control with the advantage that one admixes continuously,thus without breaks. Here too one may provide an overriding controlwhich for example counts the received impulses after hours or days,determines the nominal volume of the whole metering delivery flow fromthis and compares this to the actual metering delivery flow deliveredaccording to the control and where appropriate corrects this. Theoverriding correction may advantageously be carried out after a fewimpulses or after carrying out one or more pump strokes. Furthermore thecontrol has the usual safety circuits which for example ensure that themetering delivery flow is adapted given excessively large deviations inthe main delivery flow, e.g. is stopped if after a predefined time onereceives no further impulse.

1. A method for activating an electric motor of a metering pump, withwhich a fluid quantity to be delivered is predefined by way of anexternal impulse trigger, wherein a predetermined delivery quantity isallocated to each impulse, characterized in that the temporal intervalof at least two impulses is detected and the electrical motor isactivated such that the fluid quantity to be delivered, taking apreviously evaluated interval as a basis, is distributed over asubstantial impulse interval according to a predefined course, and thepump motor is not activated to deliver fluid until the receipt of atleast two impulses.
 2. A method for activating an electric motor of ametering pump, said method comprising the steps of: predefining aquantity of fluid to be delivered by an external impulse trigger to theelectric motor; allocating a predetermined delivery quantity to theexternal impulse; detecting an interval between at least two impulses;activating the electric motor for a period of time using said interval:determining a missed quantity resulting after the activation of two ormore successive impulse intervals; correcting for said missed quantityin subsequent impulse intervals; and activating the pump motor toperform said correcting step only after receiving at least two impulses.